Preparation of 2,4-bis(hexafluoroisopropylidene)-1,3-dithietane by reaction of perfluoroisobutene with selected alkali metal salts

ABSTRACT

Disclosed herein is a process for preparing 2,4bis(hexafluoroisopropylidene)-1,3-dithietane by reacting perfluoroisobutene with alkali metal salts of selected organic sulfur-containing acids at temperatures of about -80* to 150* C.

waited States Patent England et al.

[ PREPARATION OF 2,4-

BIS(HEXAFLUOROISOPROPYLIDENE) 1,3-DITHIETANE BY REACTION OF PERFLUOROISOBUTENE WITH SELECTED ALKALI METAL SALTS Inventors: David C. England; Maynard S. Raasch; William Arthur Sheppard, all of Wilmington, Del.

Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

Filed: Feb. 16, 1971 Appl. No.: 115,745

US. Cl. ..260/327 M Int. Cl. ..C07d 69/00 Field of Search ..260/327 M 51 Sept. 26, 1972 [56] References Cited Primary Examiner-Henry R. Jiles Assistant Examiner-Cecilia M. Shurko Attorney-James A. Costello S 7] ABSTRACT Disclosed herein is a process for preparing 2,4- bis(hexafluoroisopropylidene)-1,3-dithietane by reacting perfluoroisobutene with alkali metal salts of selected organic sulfur-containing acids at temperatures of about -80 to 150 C.

7 Claims, N0 Drawings PREPARATION OF 2,4- BIS(HEXAFLUOROISOPROPYLIDENE)A(C DITIIIETANE BY REACTION OF PERFLUOROISOBUTENE WITH SELECTED ALKALI METAL SALTS BACKGROUND OF THE INVENTION l. Field of the Invention This invention concerns a new process for preparing 2,4-bis(hexafluoroisopropylidene)-l ,3-diethie'tane which is the dimer of bis( trifluoromethyl)thioketene.

2. Description of the Prior Art The compound 2,4-bis(hexafluoroisopropylidene)- l,3-diethietane is disclosed in M. S. Raasch, U. S. Pat. No. 3,275,609, along with a process for its preparation according to the equation wherein R is a lower alkyl group.

D.C. England, U. S. Pat. No. 3,544,591, discloses in the most pertinent aspect, making 2,4-bis(hexafluoroisopropylidene)-l ,3-dithietane by the following process perfiuorisoalkali butane metal (when X=F) sulfide (CFa)zC=C C==C(CF3)2 Unlike the reaction mechanisms of the England patent, the novel process taught herein does not rely on the formation of sulfide ion from the sulfur-containing starting material. No sulfide ion is formed in the novel process and the reaction proceeds by a different route.

In Knunyants, et al., Russian Pat. No. 246,508, the dithietane is prepared by reacting perfluoroisobutene with thioacid salts such as potassium diethylthiophosphate,

potassium thiocyanate, KSCN, and sodium thiosulfate, Na S- O? The potassium diethylthiophosphate has its sulfur covalently bonded to phosphorus and the other two are inorganic salts.

SUMMARY OF THE INVENTION A process has now been discovered for the preparation of 2,4-bis( hexafluoroisopropylidene )-l ,3- dithietane by the reaction of perfluoroisobutene with an alkali metal salt of an organic sulfur-containing acid in which the metal is ionically bonded to sulfur that is in turn covalently bonded to carbon.

The contemplated alkali metal salts of organic sulfurcontaining acids are characterized by their capacity to ionize at the metal-sulfur bond to yield an alkali metal cation and a monovalent organic anion with its charge associated with sulfur.

The salts have the formula wherein:

M= lithium, sodium, potassium, rubidium or cesium, Q= S, O, or N-C H A= NRR, OR, SM, or R, R alkyl of up to eight carbon atoms or phenyl, R R or H, and R alkyl of up to eight carbon atoms.

When:

and

A= NRR the salt is a dithiocarbamate, A= OIQ, the salt is a xanthate, A =SM, the salt is a trithiocarbonate, A R, the salt is of a dithioacid.

When:

Q O I and A= NRR the salt is a monothiocarbamate,

A SM, the salt is a dithiocarbonate,

A-= R, the salt is of a monothioacid. When:

Q NC H and A NRR, the salt is of a trisubstituted thiourca, Q a s and A R, the'salt is of a thioamide.

It is noted that the alkyl groups of up to eight carbon atoms in R and R can be straight, cyclic or branched chain structures.

The preferred salts are the alkali metal dithiocarbamates (in which Q S and A NRR With their use the best yields of 2,4-bis(hexafluoroisopropylidene)- l,3-dithietane are obtained. See, for instance, Example 2 where a 68 percent yield is obtained.

The process of the invention may be carried out at temperatures in the range from to C. Preferred temperatures are in the range from 25 to C., especially that portion of the range between 25 to 5 C., which latter temperature is the boiling point of perfluoroisobutene.

DETAILS OF THE INVENTION The process of the invention may be carried out neat by contacting the selected alkali metal salt with perfluoroisobutene, the latter preferably in liquid state. However, the reaction is exothermic and it is preferred practice to carry it out in the presence of a reaction medium which is inert to the reactants and products. The reaction medium assists in dissipating the heat of reaction and provides good contact between the reactants.

The preferred media are aprotic liquids in which perfluoroisobutene and the selected salt are at least somewhat soluble. Thus, there may be employed water, ethers such as diethyl ether, ethylene glycol dimethyl ether (glyme), diethylene glycol dimethyl ether (diglyme) and tetrahydrofuran; nitrohydrocarbons such as nitromethane, nitroethane and nitrobutane; N,N-disubstituted amides such as dimethylformamide and diethylacetamide', organic nitriles such as acetonitrile and benzonitrile and mixtures of these.

Time and pressure are not critical reaction variables. When a liquid reaction medium is used, the reaction is essentially complete by the time the reactants have all been brought in contact. Small increases in yield of product may be obtained by allowing the reaction mixture to stand for periods of from one-half hour to one hour before recovery of the product. Pressures both above and below atmospheric pressure may be employed. Preferred pressures are atmospheric and slightly elevated pressures, i.e., up to 10 atmospheres such as might be obtained from autogenous pressure of perfluoroisobutene when the reaction is carried out in a closed reactor.

The proportions of the reactants which may be brought together to effect the process of this invention may be varied widely. For example, molar ratios of perfluoroisobutene: alkali metal salt from 1:20 to 20:1 may be employed. However, it is preferred not to use perfluoroisobutene in excess amounts because perfluoroisobutene is toxic and may have to be eliminated from the final product. Equimolar proportions of the reactants are preferred. The reaction is suitable for carrying out on either a batch or continuous basis.

2,4-Bis(hexafluoroisopropylidene)-1,3-dithietane is a crystalline solid which melts at about 85 C. and boils at 170 C. at atmospheric pressure. It may be recovered from the reaction mixture of the present invention by known means such as by distillation, sublimation, crystallization and the like. It may be purified by sublimation or by recrystallization from a suitable solvent such as petroleum ether, carbon tetrachloride or hexane.

The 2,4-bis(hexafluoroisopropylidene)-1,3- dithietane has high thermal stability (up to about 400 C.) and is useful, inter alia, as a heat transfer medium.

It is also useful in the synthesis of bis(trifluoromethyl)thioketene monomer.

SPECIFIC EMBODIMENTS In the Examples which follow, parts are by weight unless otherwise indicated. These Examples are meant to illustrate but not to limit the invention.

EXAMPLE 1 A mixture of 3.3 g of N,N-diethyldithiocarbamic acid sodium salt, 3 ml of diethylene glycol dimethyl ether and 9 g of perfiuoroisobutylene was sealed in a Carius tube at liquid nitrogen temperature. On melting and mixing at room temperature an exothermic reaction occurred. After standing 0.5 hour the tube was cooled, opened and the contents poured into water. The heavy oil which separated was distilled under reduced pressure to give 2.2 g of (C H NCSF, bp 70 C./2 mm. Crystals of 2,4-bis(hexafluoroisopropylidene)-l,3- diethietane collected in the -78 C. trap attached to the still.

4 EXAMPLE 2 A mixture of 113 g (0.5 mol) of N,N-diethyldithiocarbarnic acid sodium salt trihydrate and 300 ml of ethylene glycol dimethyl ether (glyme) was stirred in a three-neck flask fitted with a dry ice-cooled condenser and thermometer while adding as gas 98 g (0.49 mol) of perfluoroisobutylene, keeping the temperature at C. to 0 C. by cooling. When addition was complete, the mixture was allowed to come to room temperature with stirring and then poured into cold dilute sulfuric acid. The heavy oil was diluted with methylene chloride, washed three times with water, dried over magnesium sulfate, filtered and methylene chloride removed by distillation. The resulting oil was cooled in ice and crystals which separated were filtered to give 42 g of 2,4-bis(hexafluoroisopropylidene)-1,3- dithietane, mp 8385 C. A mixed melting point with material made from perfluoroisobutylene and potassium sulfide showed no lowering. Distillation of the filtrate caused an additional 23 g of the dithietane to sublime (mp 78-83.5 C.) making the total yield 65 g (68 percent). The distillation also gave 44 g (66 percent) of (C H NCSF, bp 45 C./0.9 mm. It was characterized by nmr and analyses.

Anal. Calcd. for C H NSF:

C, 44.48; H, 7.47; N, 10.38; S, 23.75; Found: C, 44.33; H, 7.39; N, 10.31; S, 23.82;

EXAMPLE 3 The procedure of Example 2 was repeated except that one-half the amount of perfluoroisobutylene was used (45 g). The yield of dithietane was 22 g (46 percent) obtained by filtration.

EXAMPLE 4 EXAMPLE 5 A mixture of 16 g (0.1 mol) of potassium ethyl xanthate and 150 ml of glyme was stirred in a threeneck flask fitted with a dry ice-cooled condenser and thermometer while adding as gas 22.5 g (0.11 mol) of perfluoroisobutylene. Reaction was exothermic and the mixture was kept at about 0 C. with cooling. Stirring was continued after addition of gas was complete until the temperature of the mixture reached 20 C. It was then poured into cold, dilute sulfuricacid and filtered. Recrystallization from petroleum ether gave in successive crops 1.7 g, mp -84C; 4.9 g, mp 79-82 C.; 7.1 g, mp 5255 C. and 0.8 g, mp 5 l54 C. The first two crops (6.2 g, 34 percent) were characterized by mixed melting point and infrared as 2,4-bis( hexafluoroisopropylidene)-1,3-dithietane and the last two as largely C 11 OC(S)SC(S)OC H EXAMPLE 6 A dark red aqueous solution of potassium trithiocarbonate, (KS CS, was prepared as described in Organic Syntheses, Collective Vol. IV, p. 967. A mixture of 40 g (ca, 0.1 mol) of this solution and 150 ml of glyme in a three-neck flask fitted with a thermometer and dry icecooled condenser was stirred while adding 22.5 g (0.1 1 mol) of perfluoroisobutylene at about C. When addition was complete the mixture was allowed to come to room temperature and poured into dilute acid. The heavy oil which separated was cooled in an ice bath. Crystals which separated were recrystallized from petroleum ether to give 3.2 g (16 percent) of 2,4- bis(hexafluoroisopropylidene)-1 ,3-dithietane.

When sodium dithiocarbonate, (NaShCO, is substituted for potassium trithiocarbona'te in the procedure of Example 6, a similar yield of 2,4-bis(hexafluoroisopropylidene)-1,3-dithietane is obtained.

EXAMPLE 7 A mixture of 45 g.(0.25 mol) of N,N-dimethyldithiocarbamic acid sodium salt dihydrate in 150 ml of glyme was reacted with 51 g (0.25 mol) of perfluoroisobutylene as described for Example 2. The yield of 2,4-bis(hexafluoroispropylidene)-l ,3- dithietane was 28 g (56 percent).

EXAMPLE 8 When the procedure of Example 7 was repeated using the impure perfluoroisobutylene (81 g of 68 percent purity) described in Example 4, the yield of 2,4- bis(hexafluoroisopropylidene)-l,3-dithietane was 26 g (52 percent).

EXAMPLE 9 A mixture of 18.8 g (0.1 mol) of potassium tertbutylxanthate in 150 ml of glyme was stirred in a threeneck flask fitted with a dry ice-cooled condenser and thermometer. Perfluoroisobutylene (20 g, 0.1 mol) was added as gas, keeping the temperature at -l0 to C. When addition was complete, the mixture was heated to reflux, cooled and poured into dilute sulfuric acid. The heavy red oil which separated was cooled, filtered and the solid recrystallized from petroleum ether to give 2 g (10 percent) of 2,4-bis-(hexafluoroisopropylidene)-l ,3-dithietane, mp 8184 C.

EXAMPLE 10 A mixture of 18 g (0.1 mol) of N-ethyldithiocarbamic acid sodium salt dihydrate in 150 ml of glyme was reacted with 20 g (0.1 mol) of perfluoroisobutylene and worked up as described in Example 2. On addition of the reaction mixture to dilute sulfuric acid a solid separated. It was filtered and air-dried (6.4 g). Recrystallization from carbon tetrachloride gave a mixture of crystals, mp 81-l10 C. Presence of 2,4- bis( hexafluoroisopropylidene)-1 ,3-dithietane was indicated by the characteristic crystal plates and confirmed by infrared absorption analysis.

EXAMPLE 11 Perfluoroisobutylene (20 g, 0.1 mol) was reacted with N,N-dimethyldithiocarbamic acid sodium salt dihydrate (18 g, 0.1 mol) and worked up as described for Example 2. In three separate experiments there was used as solvent, respectively, (1) a mixture of 25 ml of water with 25 ml of glyme, (2 50 ml of tetrahydrofuran, and (3 50 ml of glyme. The 2,4-bis(hexafluoroisopropylidene)-1,3-dithietane product was filtered from the dilute sulfuric acid and air-dried to give respective yields of 4.4 g (23 percent), 4.1 g (22 percent) and 7.7 g (40.5 percent).

EXAMPLE 2 A mixture of 20 g (0.1 mol) of N,N-diisopropyldithiocarbamic acid sodium salt in 50 ml of glyme was stirred in a 3-neck flask fitted with a thermometer and dry ice-cooled condenser. Perfluoroisobutylene (20 g, 0.1 mol) was added as gas at 10 to +13 C. When the addition was complete the mixture was stirred at 0 C. for 0.5 hour. It was then poured into a cold solution of 50 ml of concentrated sulfuric acid in 200 ml of water. Solids were collected by filtration and air-dried to yield 12 g of mixed crystals, mp 77-96 C. They were recrystallized from hexane to'give 5.2 g, mp 8394 C., and from the oily filtrate there was recovered by recrystallization 1.8 g of crystalline plates of 2,4- bis( hexafluoroisopropylidene )-l ,3-dithietane, mp 83-84 C.

EXAMPLE l3 Perfluoroisobutylene (20 g, 0.1 mol) was reacted with a mixture of 23 g (0.1 mol) of N,N-dibutyldithiocarbamate sodium salt in 50 ml of glyme according to the procedure described for the diisopropylcarbamate in Example 12. The yield of 2,4-bis(hexafluoroisopropylidene)-l,3-dithietane, mp -82 C., was 6.2 g (31 percent).

EXAMPLE 14 A mixture of 9 g (0.05 mol) of C H COSK (potassium salt of thiobenzoic acid) and 25 ml of glyme was kept at 0 to -l0 C. and stirred in a three-neck flask fitted with a thermometer and dry ice-cooled condenser While adding as gas 11 g (0.055 mol) of perfluoroisobutylene. When addition was complete, stirring was continued for 0.5 hour at 0 C., and the mixture was then poured into a solution of 54 ml ,of concentrated sulfuric acid in 200 ml of water. The heavy layer which separated was diluted with methylene chloride, washed with water, dried over magnesium sulfate, filtered and methylene chloride removed by distillation. The mixture was then cooled and, 1.2 g of white crystals filtered off. Distillation of the filtrate caused additional crystals to sublime in the still. All crystalline material was combined and recrystallized from petroleum ether to give 1.1 g (11 percent) of 2,4- bis( hexafluoroisopropylidene )-l ,3-dithietane, mp 8 l-84 C. lt was characterized by infrared absorption analysis and by mixed melting point with an authentic sample.

When the sodium salt of dithiobenzoic acid (C l-l CSSNa) is substituted for potassium thiobenzoate in the procedure of Example 14, a similar yield of 2,4-bis-(hexafluoroisopropylidene)-1,3- dithietane is obtained.

EXAMPLE 15 Perfluoroisobutylene (l l g, 0.055 mol) was reacted with 6 g (0.05 mol) of CH COSK (potassium salt 01" thioacetic acid) in 25 ml of glyme using the same conditions as described in Example 14. From the product mixture there was recovered 0.1 g of crystalline 2,4- bis( hexafluoroisopropylidene)-l ,3-dithietane, mp

8l83 C. (from petroleum ether). It was characterized by mixed melting point and infrared absorption analysis.

When the sodium salt of dithiobutyric acid (C l-l CSSNa) is substituted for potassium thioacetate in the procedure of Example 15, a similar yield of 2,4- bis(hexafluoroisopropylidene)-1,3-dithietane is obtained.

EXAMPLE 16 Perfluoroisobutylene (11 g, 0.055 mol) was reacted with 8 g (0.059 mol) of (CHQ NCOSK (potassium salt of N,N-dimethylmonothiocarbamic acid) in 25 ml of glyme using the same conditions as described in Example 14. The oily product was distilled. Material which distilled around 130 C. (5.9 g) solidified and was recrystallized from petroleum ether to give 3.3 g (34 percent) of pure 2,4-bis(hexafluoroisopropylidene)- l,3-dithietane, mp 83-85 C. It was characterized by mixed melting point and infrared absorption analysis.

EXAMPLE 17 EXAMPLE 18 A mixture of 11.5 g (0.05 mol) of C H NHCSNHC H (thiocarbanilide) in 50 ml of glyme was stirred and cooled at -l0 C. while adding slowly 2.5 g (0.05 mol) of sodium hydride as a 50 percent suspension in mineral oil. When reaction was complete (hydrogen evolution and disappearance of gray color with the formation of the sodium salt of thiocarbanilide) stirring and cooling were continued while adding 1 l g (0.050 mol) of perfluoroisobutylene as gas. When addition was complete stirring was continued for 1 hour at 0 C. The mixture was then poured into dilute sulfuric acid causing a gummy solid to separate. This solid was extracted with warm petroleum ether and the ether removed by distillation. The mixture was cooled in ice, filtered and recrystallized to give 2 g (20 percent) of pure 2,4-bis( hexafluoroisopropylidene)- 1 ,3-dithietane, mp 83-85 C. It was characterized by mixed melting point and infrared absorption analysis.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A process for preparing 2,4-bis(hexafluoroisopropylidene)- l ,3-dithietane comprising reacting, at a temperature of to C., perfluoroisobutene with an alkali metal salt of the formula wherein:

M =lithium, sodium, potassium, rubidium or cesium,

Q =8, 0 or NC H R alkyl of up to eight carbon atoms or phenyl,

R R or H, and

R alkyl of up to eight carbon atoms.

2. A process according to claim 1, carried out in the presence of an aprotic liquid medium.

3. A process according to claim 1, employing equal molar proportions of perfluoroisobutene and alkali metal salt.

4. A processaccording to claim 1, employing equal molar proportions of perfluoroisobutene and alkali metal salt at a temperature in the range of 25 to +5 C., in the presence of an aprotic liquid medium.

5. A process according to claim 1, wherein Q S, and A NRR 6. A process according to claim 5, wherein Q S, A NRR and R=R=ethyl.

7. A process according to claim 5, wherein Q S, A NR R and R R methyl.

' UJNH'EU enema KAHLNJL Utrnmt.

u i 2 1: e 1 w Patent N.o. 3 e9e,e6o Dated pt r 26, 1972 David C. England,

Inventofls) Maynard S. Baasch and flilliam Arthur Sheppard It is certified that error appears in the above-Mentified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 2, "MC" should be l,3-

" line 57; "O should Col. 2, line 50; "+C" should. be +25C 001. 1+, line), "-90-" should b -Q -1oc Signed and seieled this 20th day of November 1973.

(SEAL) Attest: v V

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer 7 Acting Commissioner of Patents 

2. A process according to claim 1, carried out in the presence of an aprotic liquid medium.
 3. A process according to claim 1, employing equal molar proportions of perfluoroisobutene and alkali metal salt.
 4. A process according to claim 1, employing equal molar proportions of perfluoroisobutene and alkali metal salt at a temperature in the range of -25* to +5* C., in the presence of an aprotic liquid medium.
 5. A process according to claim 1, wherein Q S, and A NR1R2.
 6. A process according to claim 5, wherein Q S, A NR1R2 and R1 R2 ethyl.
 7. A process according to claim 5, wherein Q S, A NR1 R2 and R1 R2 methyl. 